The term full duplex data communication as used herein is intended to mean the simultaneous transmission of data in both directions over a communication means, in this case an optical fiber, i.e. a filament that provides a two way path for data-containing light to travel between the two ends of the filament.
It is known in the art to provide semiconductor means that is operable to inject data-containing light into one end of an optical fiber, and to provide semiconductor means that is operable to detect the data-containing light that issues from the other end of the fiber.
For example, U.S. Pat. No. 4,733,094 describes a bidirectional or full duplex optoelectronic arrangement wherein a discrete (i.e. individually distinct) LED and a discrete photodiode are mounted side by side within a box. One or more mirrors are provided so that the LED and the photodiode are capable of simultaneously emitting light to an optical fiber, and receiving light from the optical fiber.
U.S. Pat. No. 4,773,074 describes a unitary emitter-receiver semiconductor diode device for direct coupling to an optical fiber. In this unitary structure, a double heterostructure diode and a waveguide photodiode are selectively switched between a light emission mode of operation or a light receiving mode of operation. Application of a reverse bias causes the device to operate as a light receiver. Application of a forward bias causes the device to operate as a light emitter. U.S. Pat. No. 4,948,960 is generally similar in its teaching.
A feature of the present invention is the use of an integrated, single unit, semiconductor light emitting device that is mounted on top of a photodiode. Of interest in this regard is the publication Proceedings of the IEDM 89, 1989, at pages 543-546, which describes an electroptic device that consisting of a light emitting device (LED) mounted on top of a photodiode, to form a unitary semiconductor structure. This publication is incorporated herein by reference for the purpose of indicating the background of the invention.
Also of general interest is U.S. Pat. No. 4,766,471 which shows a light transmissive conduit that is formed to interconnect a light emitter and a light detector.
In addition, U.S. Pat. No. 4,851,695 discloses an optoelectronic coupling element wherein an infrared semiconductor light emitting chip is mounted on top of an infrared semiconductor light receiving chip, to thereby form a unitary coupling element; U.S. Pat. No. 4,857,746 describes an optocoupler wherein a substrate member is fabricated to contain a light transmitter and a light receiver; and U.S. Pat. No. 4,967,241 discloses a unitary semiconductor light emitting device and photosensor, the light emitting device being associated with an optical fiber cable and operating to inject light into the end of the optical fiber.
In the device of U.S. Pat. No. 4,967,241, a semiconductor substrate member is fabricate to have the light emitting device on the bottom surface thereof, and to have an upwardly extending open window therein. The light emitting device emits light in an upward direction, through this window and into the end of the optical fiber. A photosensor is formed in the side wall of this window, so as to receive a portion of the light that is generated by the light emitting device. The resulting output signal that is provided by the photosensor is connected as one input to a differential amplifier, and the output of the differential amplifier operates to maintain the light output of the light emitting device constant.
While the devices of the prior art as exemplified above are generally acceptable for their intended purposes, the need remains for a physically compact semiconductor optoelectronic device that provides for full duplex data communication over a single optical fiber in a reliable and an efficient manner.